The present invention relates to an aerated frozen product having low fat content. More particularly, the invention relates to an aerated frozen dessert product having low fat content wherein at least part of the fat is present in the form of platelets and which achieves physical and sensory properties more commonly associated with higher fat products.
Frozen aerated products such as ice cream are complex mixtures, which are often defined in terms of continuous and dispersed phases. The continuous phase is a combination of an unfrozen solution, a fat emulsion and a suspension of solids in liquid. Water, sugar, hydrocolloids, proteins and other solubles make up the unfrozen solution. Suspended in the aqueous phase are insoluble solids, including ice crystals, and milk solids. The continuous phase also consists of dispersed air bubbles, or foam.
The ingredients and processing variables used in its production dictate the characteristics of this mixture and therefore the aerated product""s sensory attributes. Quality ice cream, for example, should possess a smooth and creamy mouthfeel resulting from a high level of homogeneity of the components. An ice cream""s texture refers to its smoothness and is perceived whilst the ice cream is being manipulated in the mouth. The characteristic is directly related to the size of the crystalline material present. Most of the fat and water present is in the crystalline state, but ice crystals and air cells form a coarser dispersion than that of fat globules. The roughness observed when perceptible crystals are present is generally felt to be a sign of diminished quality.
In addition to controlling the extent of crystallisation in the frozen aerated product, the physical properties of frozen ice cream complex must be controlled for a quality ice cream. Such a product should not melt away too quickly at ambient temperature so as, for example to retain its firmness to the spoon for the period of its consumption. However, the product must melt when exposed to elevated temperatures and in particular should exhibit a gradual and controlled melting behaviour when put in the mouth upon eating.
Air cell stability and size in the aerated frozen product influence that product""s meltdown characteristics and mouthfeel. After ice cream has been extruded, for example, the stability and size of the cells depend on the mechanical properties of the air interface and the properties of the medium surrounding the cells. The interface comprises emulsifiers, such as proteins, fat globules and agglomerated fat globules or droplets. On account of their shape, globules are typically equated with xe2x80x9cspheresxe2x80x9d and innumerable shapes can be formed from combination of those globules as they agglomerate. However, the partial protrusion of these globules and agglomerates from the interface together with fat completely dispersed in the continuous phase also indirectly stabilize the aerated product.
These fat agglomerates are formed during the processing of ice cream emulsion. Fat present in the pre-mix (simply the mixture of ice cream ingredients before the steps of homogenization and pasteurisation) is emulsified when that pre-mix is homogenized to form fat globules. The extent of emulsification depends on the type of fat, proteins and other emulsifiers present in the pre-mix. Typically the homogenized mixture containing emulsified fat is then pasteurised to form what is known in the art as the xe2x80x9cmixxe2x80x9d, aged for a period of time, and later frozen, aerated and extruded. The actual agglomeration of emulsified fat occurs during the later freezing and aerating process.
Emulsifying ingredients must be chosen to allow this fat agglomeration to occur. The possibility of obtaining too much agglomeration (resulting in an oily sensation upon eating the final aerated product) and no agglomeration (resulting in a poor structure for the product) is considerable.
Small molecular emulsifiers control the extent of fat agglomeration by partially destabilizing the fat globule membrane. Although there are a number of suitable food grade emulsifiers, fatty acid monoglyceride and diglyceride esters are commonly used.
During the ageing time of the mix used to form the aerated product, the action of the small molecule emulsifiers causes protein rearrangement at the oil/water interface, and some protein is desorbed. The state of the interfacial layer at the end of this ageing time will determine the stability of the fat globules to the subsequent shear and aeration process. The lower the emulsion stability, the more fat agglomeration that will result during processing. During ageing of the mix, some liquid fat present will crystallise. This crystallisation process does not, however, lead to any significant change in the geometry of the fat globule.
Since the beginning of the 1980s there has been an increasing demand for confectionery products and desserts such as ice cream and related products which have a reduced calorific value.
Reducing the amount of fat in the ice cream would be the most effective way of reducing the calorific value as it has a calorific value per gram which is higher than that of carbohydrates. By reducing the amount of fat in the ice cream, considerable difficulties arise as its effectiveness in stabilising the structure is reduced. Further, key sensory attributes of ice cream such as creamy texture, mouthcoating and thickness are dominated by the flow behaviour of the aerated product during melting; changes to the fat content alters the viscosity of the mix and the air cell structure of the aerated product.
To compensate for reduced stability as the content of the fat is reduced, solutions would include using polysaccharide as a stabilizer and modifying the proteins (which are also adsorbed in the air cell interface). These changes to formulation have unsatisfactory results for the taste and texture of the ice cream. An alternative solution is to replace the typical fats of ice cream (triglycerides) with a fat simulating material. WO91/11109 (Whelan et al.) discloses replacement of fat with polyol fatty acid polyesters having at least four fatty acid groups, each group containing from 2 to 24 carbon atoms. These polyesters retain the organoleptic properties of the ice cream but have the disadvantage that they either have an undesirable laxative effect or give a waxy mouthfeel.
Recently, homogenisation technologies have been utilized in the ice cream industry to decrease the size and increase the number of fat globules in the ice cream product. This provides better distribution of the available fat in the fat-reduced product. However, to maintain maximum functionality of the small oil droplets the emulsifier system needs to be adjusted (as described in Barfod N. M. et al. xe2x80x9cEffects of Emulsifier on Protein-Fat interactions in the Ice Cream Mix during Ageing: Quantitative Analysisxe2x80x9d Fat Science and Technology 93 (1991) 24-29) and severe shear conditions such as those applied by low temperature extrusion are advantageous. Such technologies are not readily available and are expensive.
It is therefore an object of the invention to provide an aerated frozen product having low fat content but high stability and meltdown resistance at ambient temperatures.
It is another object of the invention to provide an aerated frozen product that exhibits controlled and gradual meltdown when exposed to the temperatures of the mouth upon eating.
It is also an object of the invention to provide an aerated frozen dessert product having low fat content that has a thick and creamy mouthfeel.
It is a further object of the invention to provide an aerated frozen product that can be produced economically using readily available technologies.
These and other objects of the invention are achieved by the present invention which comprises an aerated frozen product comprising less than 8% fat by weight and characterized in that the aerated frozen product comprises fat platelets, and after it has been melted and cooled comprises fat platelets and spherical fat globules at a platelet to sphere ratio of greater than 0.02.
In this invention the spherical fat globules as known in standard mixes are replaced in part by fat platelets such that the fat platelets co-exist with the globules and agglomerates in the mix and the frozen aerated product.
[The term spherical fat globules includes both individual droplet and agglomerates formed from these droplets as known in standard mixes. All such globules, identified by a spherical fracture when viewed under Transmission electron microscopy as described hereinafter, are included in determining the platelet to sphere ratio.]
It has been shown by Scanning Electron Microscopy that such platelets exist in both the lamella surrounding the air cells and in the continuous phase of the aerated frozen product. The platelets improve the homogeneity of the continuous phase and the temperature tolerance of the frozen aerated product when compared to standard frozen aerated products containing that level of fat and not including fat platelets.
In accordance with a first embodiment of the present invention there is provided an aerated frozen product comprising less than 8% fat by weight and characterized in that the aerated frozen product comprises fat platelets, and after it has been melted and cooled comprises fat platelets and spherical fat globules at a platelet to sphere ratio of greater than 0.02, the aerated frozen product also satisfying the condition that percentage mass loss after 120 minutes is less than 90% at 20xc2x0 C.
In accordance with a second embodiment of the present invention there is provided an aerated frozen product comprising less than 8% fat by weight and characterized in that the aerated frozen product comprises fat platelets, and after it has been melted and cooled comprises fat platelets and spherical fat globules at a platelet to sphere ratio of greater than 0.02, the aerated food product also satisfying the condition that the percentage mass loss after 120 minutes is less than 100% at 37xc2x0 C.
Preferably the platelet to sphere ratio is greater than 0.05. More preferably the platelet to sphere ratio is greater than 0.6. It is most preferred that the platelet:sphere ratio is greater than 0.1.
Preferably the frozen aerated product comprises less than 6% fat by weight. More preferably the product comprises less than 4% fat by weight.
Preferably the frozen aerated product is manufactured at an overrun of between 30% and 200% and more preferably at an overrun between 50 and 150% (wherein overrun is defined in xe2x80x9cIce creamxe2x80x9d by W. S. Arbuckle, Ari Publishing, 1972, p194.)
A preferred component of the frozen aerated product is the emulsifier, which is present to disperse the fat particles. Also the emulsifiers facilitate air incorporation during freezing to provide a finer dispersion of air cells that imparts a smoother body and texture and slower meltdown to the resulting aerated product. The particular amount of emulsifier that is effective will depend on the type of emulsifier and the particular composition of the frozen product. Preferably, the aerated frozen product comprises from about 0.05 to 0.2% non-protein, small molecular emulsifier by weight.
As is known in the art, the pre-mix of frozen product, before it is processed to form the aerated frozen product, comprises an oil-in-water emulsion whereby some emulsifiers are present at the oil-water interface, and others are present in the bulk fat phase. For the formation of fat platelets during aging of such pre-mixes it is preferred that the fat type must have a relatively high solid: liquid ratio in the fat phase present at the aging temperature. Secondly, the fat used must have the habit of forming large crystals within the bulk fat phase, a feature that is not only dependent on fat type but also the additives, such as emulsifiers, which are present. Also it is preferred that the fat and emulsifier and other additives which are to be included in the oil-water interface are chosen such that the interfacial tension of the oil-water interface present in the pre-mix is low enough to allow for the transition from sphere to platelet.
It is preferred that the frozen aerated product comprises an effective amount of fat selected from the group consisting of hardened coconut oil, palm kernel oil, hardened soy bean oil and rape seed oil.
It is preferred that the emulsifier comprises monoglycerides of unsaturated fatty acids hereinafter referred to as unsaturated monoglycerides. The degree of saturation of fatty acids and derivatives thereof is normally quantified by the iodine value (IV). The iodine value is defined as the number of grams of iodine adsorbed by 100 grams of fat or oil. Fatty acids and derivatives having iodine values greater than 3 are understood to be at least partially unsaturated whereby partly means a mixture of saturated and (mono- or poly-unsaturated) fatty acids or derivatives. It is preferable that the monoglycerides used in the present invention have an iodine value greater than 50.
Although the invention is disclosed with specific reference to ice cream, it is to be understood that the term frozen aerated product includes all suitable products. In circumstances where the fat is not conventionally present in an aerated frozen product, but is included for textural reasons, that product falls within the scope of the present invention.
The frozen aerated product of the present invention may also comprise other compounds and ingredients, which may be selected from water, stabilisers, sweeteners such as sucrose, and proteins.
Water provides a continuous aqueous phase in which emulsified fats may be dispersed or suspended. Upon freezing the aqueous phase provides ice crystals. The source of water may be added water or it could be supplied from fluid ingredients such as those used to supply milk solids other than fat. The level of water can be varied according to the structural properties desired, and the level of other components. Usually aerated frozen products comprise 50 to 75% water by weight.
Stabilisers are typically present in aerated frozen products although it is noted in particular that the stabilising effects of the fat platelets may allow for stabiliser replacement in a number of frozen aerated product applications. Suitable stabilisers include alginates, gelatin, gum acacia, guar gum, gum karaya. Locust bean gum, carageenan and salts thereof, xanthan gum, microcrystalline cellulose, cellulose ethers or mixtures thereof. The amount of stabiliser is preferable less than 1% by weight.
The frozen aerated products of the invention may form part of any composite food product such as for example coated ice cream or an ice cream filled wafer. Further the aerated frozen product may comprise other conventional food product ingredients such as those selected from natural or artificial colourants, flavour extracts, essences or concentrates, whole or comminuted fruit or nut pieces and couvertures as appropriate.
The frozen aerated products of the present invention may be produced by conventional methods used for the product concerned. For example, low fat ice creams may be produced using conventional ice cream production methods including those having homogenisation and/or pasteurisation steps. In such methods, the inclusion of air typically occurs at the same time as the product is frozen. Although the fat platelets that are present may increase the viscosity of the product before aeration, aeration of the product at the preferred levels of platelets can still be achieved using, for example, APV Technohoy MF75 or alternative mixers such as 5-L Hobart Mixers.
FIG. 1 is a Scanning electron micrograph (SEM) of a frozen aerated product produced in accordance with the present invention. The frozen aerated product used for this SEM was made from a formulation comprising 4% by weight coconut oil (CNO) with 0.3% Hymono-7804 (H7804) the specification of which is described later. The image was recorded at a magnification of 4000.